Ray Optics and Optical Instruments · Question 26

An astronomical refracting telescope will have large angular magnification and high angular resolution, when it has an objective lens of

1. small focal length and large diameter
2. large focal length and small diameter
3. large focal length and large diameter
4. small focal length and small diameter

A beam of light from a source L is incident normally on a plane mirror fixed at a certain distance x from the source. The beam is reflected back as a spot on a scale placed just above the source L. When the mirror is rotated through a small angle , the spot of the light is found to move through a distance y on the scale. The angle is given by

1. yx
2. x2y
3. xy
4. y2x

A thin prism having refracting angle 10 is made of glass of refractive index 1.42. This prism is combined with another thin prism of glass of refractive index 1.7. This combination produces dispersion without deviation. The refracting angle of second prism should be

1. 6
2. 8
3. 10
4. 4

Match the corresponding entries of column 1 with column 2. [Where m is the magnification produced by the mirror]

1. (a)-(p) and (s); (b)-(q) and (r); (c)-(q) and (s); (d)-(q) and (r)
2. (a)-(r) and (s); (b)-(q) and (s); (c)-(q) and (r); (d)-(p) and (s)
3. (a)-(q) and (r); (b)-(q) and (r); (c)-(q) and (s); (d)-(p) and (s)
4. (a)-(p) and (r); (b)-(p) and (s); (c)-(p) and (q); (d)-(r) and (s)

An astronomical telescope has objective and eyepiece of focal lengths 40 cm and 4 cm respectively. To view an object 200 cm away from the objective, the lenses must be separated by a distance

1. 50.0 cm
2. 54.0 cm
3. 37.3 cm
4. 46.0 cm

The angle of incidence for a ray of light at a refracting surface of a prism is 45 . The angle of prism is 60 . If the ray suffers minimum deviation through the prism, the angle of minimum deviation and refractive index of the material of the prism respectively, are

1. 45 ; 2
2. 30 ; 1 2
3. 45 ; 1 2
4. 30 ; 2

Two identical glass ( g = 3/2) equiconvex lenses of focal length f each are kept in contact. The space between the two lenses is filled with water ( w = 4/3). The focal length of the combination is

1. f/3
2. f
3. 4f/3
4. 3f/4

An air bubble in a glass slab with refractive index 1.5 (near normal incidence) is 5 cm deep when viewed from one surface and 3 cm deep when viewed from the opposite face. The thickness (in cm) of the slab is

1. 8
2. 10
3. 12
4. 16

A person can see clearly objects only when they lie between 50 cm and 400 cm from his eyes. In order to increase the maximum distance of distinct vision to infinity, the type and power of the correcting lens, the person has to use, will be

1. convex, +2.25 diopter
2. concave, -0.25 diopter
3. concave, -0.2 diopter
4. convex, +0.15 diopter

A beam of light consisting of red, green and blue colours is incident on a right angled prism. The refractive index of the material of the prism for the above red, green and blue wavelengths are 1.39, 1.44 and 1.47 respectively. [figure] The prism will

1. not separate the three colours at all
2. separate the red colour part from the green and blue colours
3. separate the blue colour part from the red and green colours
4. separate all the three colours from one another